1. Technical Field
The invention relates generally to an improved suspension system for land vehicles. More particularly, the invention relates to trailing beam air suspension systems. Specifically, the invention relates to trailing beam air suspension systems whereby the trailing beams are interconnected to form a single unitary beam.
2. Background Information
With the advent following World War II of large load carrying capacity trucks and trailers in this country, came the need to provide vehicle with multiple axles for increasing the capacity of trucks over that of previously existing designs. While the use of additional axles effectively increased load-carrying capacity, it was soon realized that as the number of load bearing axles increased on a given vehicle, a number of difficulties arose. Specifically, tire scuffing, loss in fuel economy and the inability to safely corner, all work problems associated with multiple axle vehicles. Mitigation of these problems was a primary concern to the industry, which concern resulted in the development of a variety of suspension systems, both liftable and non-liftable.
Liftable suspensions could be selectively raised from the road surface or lowered into engagement with the road surface when needed, thereby mitigating a number of the aforementioned problems. Additionally, non-liftable axles have been designed for a variety of purposes, and specifically a number of specialty chassis-cab type vehicles require additional load-carrying capacity. More specifically, auxiliary suspension systems are necessary for trash compactor trucks and concrete mixing and delivery vehicles.
The transportation of goods by truck continues to be a primary method of moving goods from one location to another. This commercial success is due to the large volume and load carrying capacity available in standard chassis-cab trucks as well as in tractors which are attached via a fifth wheel to trailers. The commercial success of the trucking industry is also benefited by an extensive highway system which reaches virtually every part of North America.
Suspension systems may take a variety of forms, including parallelogram suspensions, and leading and trailing beam-type suspensions. Generally, leading and trailing beam-type suspensions include a pair of longitudinally extending beams which may be either flexible or rigid, one of which is located adjacent each of two longitudinally extending frame rails located beneath the body of the truck or trailer. These beams are pivotally connected at one end to a hanger bracket extending downwardly from the frame, with an axle extending between the beams adjacent the other end. Additionally, an air or coil spring is generally positioned intermediate each frame rail and a corresponding beam. The beam may extend forwardly or rearwardly of the pivot, thus defining a leading or trailing beam suspension respectively.
Beam-type suspension systems are used on a significant number of trucks and trailers, and must have sufficient strength to resist lateral and axial deflection while remaining stable. Lateral forces act on a suspension system in a variety of ways with the most common being that lateral forces act on a suspension as a vehicle negotiates a turn. As the vehicle turns, shear stress acts between the tire and the road surface causing a lateral stress to be transferred through the tire-wheel assembly to the axle. The axle, being rigidly attached to the suspension, transfers the lateral force into the beam causing it to deflect laterally. This lateral deflection can be extreme, and under certain loading conditions, can cause the tires to contact the vehicle frame rails.
Roll stability refers to the counter-acting forces operating on the ends of an axle causing one end of the axle to raise relative to the frame a distance greater than the other end of the axle. Roll flexibility is encountered when the vehicle frame tilts or rolls relative to the axle; for example, when the vehicle negotiates a turn such that the centrifugal and acceleration forces reduce the downward forces acting on the inside wheel of the turn, and increase the downward force acting on the outside wheel of the turn. Roll flexibility is also realized when the axle moves relative to the frame; for example, during diagonal axle walk.
Diagonal axle walk occurs when the wheels of the opposite ends of the axle encounter unlike irregularities in a road or off-the-road surface, such as when one wheel rides over a curb. As the wheel rides over the curb, an upward force acts on that wheel, and a counteracting downward force acts on the wheel not riding over the curb. If the suspension is unable to provide flexibility between the axle and the frame as the tire-wheel assembly travels over the curb or ground irregularity, or alternatively to provide flexibility between the axle and the frame as the vehicle negotiates a turn, the suspension will be too roll rigid, and may cause axle breakage or over stress vehicle components, such as the frame. As such, beam-type suspensions must be roll stable while providing sufficient vertical support to retain the vehicle above the road surface.
An additional problem associated with trailing beam type suspensions is the increased torque load which is input into the axle. More specifically, inasmuch as the beams are spaced apart a distance from 35 inches to 41 inches, and each beam pivot point receives between 20,000 and 30,000 pounds of force when engaging in roll or diagonal axle walk, with each beam length being approximately 20 inches, it is not uncommon for the axle to be subjected to 50,000 foot pounds of torque in the area intermediate the respective leading or trailing beams. The axle is thus subjected to extremely high torque loads substantially affecting the axle and its operational characteristics. Additionally, the central portion of the axle positioned intermediate the trailing beams is not reinforced, thereby further affecting the axle resistance to torque load.
The need thus exists for a suspension system which is lightweight, is roll stable, and provides adequate vertical load-carrying characteristics, and which is resistant to lateral and longitudinal axle forces. Additionally, the need exists for a suspension system which provides an axle to beam connection which is lightweight, easy to assemble, simple to manufacture and easy to align relative to the vehicle path of travel. Still further, the need exists for a suspension system which may be utilized as a tag axle, or alternatively as an auxiliary axle beneath a usual truck or trailer. The need also exists for a suspension system which substantially eliminates axle torque while strengthening the central portion of the axle.